1. Field of the Invention
The present invention relates to packages for semiconductor chips or other electronic devices.
2. Description of the Related Art
Ball grid array (BGA) packages are used for many types of semiconductor chips, including vision and micro-electromechanical (MEM) chips, for various applications. A typical BGA package for a semiconductor chip includes a printed circuit board substrate upon which the chip is mounted. The printed circuit board includes a core sheet of a glass-fiber filled epoxy laminate. Conductive metal traces are provided on upper and lower surfaces of the core layer. The chip is electrically connected to the upper traces by bond wires or the like. Metal vias electrically connect the upper and lower circuit traces through the substrate. The circuit traces on the lower surface of the substrate each extend from one of the vias to a planar metal ball land. A metal ball (e.g., solder ball) is fused to each of the ball lands. The metal balls serve as input/output (I/O) terminals for the package. A hardened encapsulant material covers the chip and a portion of the upper surface of the printed circuit board substrate.
The above-described package has numerous drawbacks. First, it is relatively expensive to make, due to the relatively complex printed circuit board substrate. Second, the contact area between each metal ball and its respective land is small, leading to decreased reliability as the contact area reduces with the finer contact pitches of successive generations. Third, the fused connection between each of the metal balls and its respective ball land is subject to shearing forces that can result in package failure due to an open circuit. Accordingly, a less expensive, more reliable package is desirable.
The present invention involves packages that include a semiconductor chip mounted on a molded plastic substrate. The molded plastic substrate includes a plurality of indentations, each having a metal lining, in a first side thereof. A plurality of reflowable metal contacts, which may be in the form of solder balls, are each placed within a respective one of the indentations and fused to the metal lining of the indentation. The reflowable metal contacts serve as I/O terminals of the package. The substrate further includes a plurality of conductive paths each electrically connected between the chip and the metal contact of a respective one of the indentations. Each indentation may further include one or more projections that are also covered by the metal lining therein. The projections extend into the metal contact.
By comparison to conventional BGA packages, the packages of the present invention avoid the high cost of a printed circuit board through the use of a molded plastic substrate. In addition, the metal contacts (e.g., balls) are protected from shearing off the substrate by their placement in the indentations. In addition, the indentations, including any projections therein, increase the metalized surface area of the substrate to which the metal balls are fused, which results in a stronger bond between the substrate of the package and the metal contacts. The present invention thus can increase package yields and package reliability compared to prior art methods.
These and other aspects and features of the present invention will be better understood in view of the following detailed description of the exemplary embodiments and the drawings thereof.